Financial Information by Business Segment - Financial Data for Business Segments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Operating revenues	$ 12,919	$ 12,354	$ 12,188
Depreciation and amortization	1,071	1,024	955
Operating income	2,209	2,244	2,339
Interest charges	591	719	604
Income taxes on operating income	589	504	594
Total assets	44,308	40,647	41,209
Construction expenditures	2,721	2,648	2,538
CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,786	10,430	10,187
Depreciation and amortization	991	946	894
Operating income	2,139	2,060	2,093
Interest charges	537	521	545
Income taxes on operating income	562	531	514
Total assets	39,637	36,258	36,885
Construction expenditures	2,132	2,135	1,909
CECONY [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	781	749	710
Operating income	1,712	1,595	1,693
Interest charges	412	402	423
Income taxes on operating income	425	380	393
Total assets	30,421	27,673	28,339
Construction expenditures	1,500	1,471	1,375
CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	132	130	120
Operating income	314	362	346
Interest charges	89	83	82
Income taxes on operating income	88	112	99
Total assets	6,530	6,008	5,925
Construction expenditures	549	536	426
CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	78	67	64
Operating income	113	103	54
Interest charges	36	36	40
Income taxes on operating income	49	39	22
Total assets	2,686	2,577	2,621
Construction expenditures	83	128	108
O&R [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	61	56	53
Operating income	128	120	123
Interest charges	35	37	31
Income taxes on operating income	35	20	28
Total assets	2,837	2,545	2,671
Construction expenditures	142	135	137
O&R [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	46	41	38
Operating income	103	87	83
Interest charges	24	25	19
Income taxes on operating income	29	13	17
Total assets	2,042	1,898	1,960
Construction expenditures	105	98	98
O&R [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	15	15	15
Operating income	25	33	40
Interest charges	10	11	10
Income taxes on operating income	6	7	11
Total assets	794	645	706
Construction expenditures	37	37	39
O&R [Member] | Other [Member]
Segment Reporting Information [Line Items]
Interest charges	1	1	2
Total assets	1	2	5
Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	19	23	8
Operating income	(60)	63	125
Interest charges	(8)	135	1
Income taxes on operating income	(8)	(41)	52
Total assets	1,026	1,314	1,061
Construction expenditures	447	378	492
Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		(1)
Operating income	2	1	(2)
Interest charges	27	26	27
Income taxes on operating income		(6)
Total assets	808	530	592
Operating Segments [Member]
Segment Reporting Information [Line Items]
Operating revenues	12,919	12,354	12,188
Operating Segments [Member] | CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	10,786	10,430	10,187
Operating Segments [Member] | CECONY [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating revenues	8,437	8,131	8,176
Operating Segments [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,721	1,616	1,415
Operating Segments [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	628	683	596
Operating Segments [Member] | O&R [Member]
Segment Reporting Information [Line Items]
Operating revenues	892	833	795
Operating Segments [Member] | O&R [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating revenues	680	628	592
Operating Segments [Member] | O&R [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	212	205	203
Operating Segments [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	1,244	1,096	1,213
Operating Segments [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	(3)	(5)	(7)
Inter-Segment Revenues [Member] | CECONY [Member]
Segment Reporting Information [Line Items]
Operating revenues	(106)	(103)	(97)
Inter-Segment Revenues [Member] | CECONY [Member] | Electric Transmission [Member]
Segment Reporting Information [Line Items]
Operating revenues	16	16	15
Inter-Segment Revenues [Member] | CECONY [Member] | Gas [Member]
Segment Reporting Information [Line Items]
Operating revenues	6	5	5
Inter-Segment Revenues [Member] | CECONY [Member] | Steam [Member]
Segment Reporting Information [Line Items]
Operating revenues	84	82	77
Inter-Segment Revenues [Member] | Competitive Energy Businesses [Member]
Segment Reporting Information [Line Items]
Operating revenues	(10)	5	8
Inter-Segment Revenues [Member] | Other [Member]
Segment Reporting Information [Line Items]
Operating revenues	$ 10	$ (5)	$ (8)